Plastic containers are widely used in a variety of applications since they can be molded easily and can be manufactured at a low cost. In particular, a bottle-shape olefin resin container that has an inner wall surface formed of an olefin resin such as a low-density polyethylene and that is formed by direct blow molding is used preferably as a container for containing a viscous, slurry-like or paste-like and less flowable liquid such as a ketchup from a standpoint that the contents can be easily squeezed out.
Usually, a bottle containing a viscous and less flowable liquid is stored in an inverted state to discharge quickly the liquid (contents) or to use up the liquid without remaining in the bottle. It is therefore desired that the viscous liquid quickly falls down without adhering to and remaining on the inner wall surface of the bottle when the bottle is inverted.
The property is desired similarly for a hollow molded article such as a hollow pipe. Usually, the hollow pipe is used to convey a viscous and less flowable liquid, and thus, it is required to make the less flowable liquid flow at a low pressure without making the liquid adhere to and remain inside the hollow pipe.
As a bottle to satisfy the aforementioned requirements, for example, Patent Document 1 proposes a multilayer structure bottle having an innermost layer formed of an olefin resin having a melt flow rate (MFR) of not less than 10 g/10 min.
The innermost layer of this multilayer structure bottle has an excellent wettability to oily contents. Therefore, when the bottle is inverted or tilted, the oily contents such as mayonnaise fall down while spreading along the surface of the innermost layer and can be discharged completely without adhering to and remaining on the inner wall surface (innermost layer surface) of the bottle.
As for the bottle for containing a viscous liquid like ketchup containing plant fibers dispersed in water, Patent Document 2 and Patent Document 3 each propose a bottle of a polyolefin resin having an innermost layer in which saturated or unsaturated aliphatic amide as a lubricant is blended.
The aforementioned Patent Documents 1-3 refer to a plastic container whose slipperiness to contents is improved by the chemical composition of the thermoplastic resin forming the inner surface of the container. Although a certain degree of improvement in the slipperiness has been achieved, the improvement in the slipperiness is limited due to the limitation of the type of the thermoplastic resin in use and the limitation of the additive, whereby any remarkable improvement has not been achieved yet.
There has been also proposed formation of a liquid layer on a surface to be in contact with a liquid. For example, a container proposed in Patent Document 4 has an inner surface, namely, a surface to be in contact with contents, which is a liquid-permeable surface, and a liquid immiscible with the contents is held on the liquid-permeable surface. Patent Document 5 proposes formation of an inner surface of a container with a resin composition including a molding resin and a liquid (a liquid immiscible with the contents).
In Patent Documents 4 and 5, a continuous liquid layer is formed on the container inner surface to be in contact with the contents, thereby improving remarkably the slipperiness to less flowable liquids, such as ketchup, sauce and mayonnaise.
Remarkable improvement in slipperiness can be achieved by the method of forming a continuous liquid layer on the inner surface of the hollow molded article such as a container to be in contact with a less flowable liquid. However, the liquid layer may drop out due to the gravity. For example, when the liquid layer is formed on the inner surface of a container like a bottle and then the bottle is held in an erected state, the liquid layer on the inner surface of the body portion falls little by little on the bottom of the container over time, and at the end, substantially no liquid layer is present on the inner surface of the body portion. By the time this container is filled with a less flowable liquid, the slipperiness of the inner surface of the body portion to the liquid may be degraded.